Jellyfish Can Help Boost Ocean's Absorption of Carbon Dioxide

As jellies die and sink to the ocean floor, they bring carbon dioxide from the surface with them.

Scientists from Germany, Spain, the United Kingdom and the United States conducted field research with the remains of jellies, more commonly known as jellyfish, and pelagic tunicates and claim that these organisms absorb human emitted carbon dioxide from the food they eat, giving the ocean more capability than previously thought to absorb CO2. The jellyfish and tunicates do so by ingesting plankton, which convert the carbon dioxide to organic carbon and other components during photosynthesis.

When the jellyfish die and sink to the bottom, that carbon goes with them and is used as food by other organisms or stored in deep water layers after decomposition. They also found that calcifying organisms also use the inorganic carbon in their calcium carbonate shells and contribute to the biological pump, the process where CO2 fixed in photosynthesis is transferred to the interior of the ocean and stored.

Click image to enlargePelagia noctiluca Photo by E-190/Wikipedia

The scientists collected various jellyfish species, including true jellies, comb jellies, and salps and videotaped the sinking process of these organisms. They were able to determine the sinking speed of each species and measured the proportion of organic carbon and nitrogen of the dry biomass and biomass weights. They found that the sinking speed of the jellyfish were higher than they had expected, at about 500 to 1600 meters a day, a speed in which the organisms can reach the bottom at a much faster rate, and without major degradation whereby decay would release CO2 higher up in the water column. The faster sinking also enables benthic organisms to consume the dead jellyfish.

They determined that the scyphozoans had the highest carbon content at 26.97 percent. Thaliaceans had 17.20 percent carbon and ctenophores had 1.40 percent. While the carbon content in jellies is smaller than that of phytoplankton, the scientists noted that their larger populations and high sinking speed delivers larger quantities of carbon to the ocean floor.

"Our dataset provides an initial overview and comparison for modelers and experimentalists to use in subsequent studies examining the role of jellies in carbon export and the efficiency of the biological pump", Lebrato said in a prepared statement. "We are continuously asked, how much organic carbon and CO2 do gelatinous plankton sink worldwide, whether their export capacities are similar to phytoplankton and marine snow. And if an increase of jellyfish in the future will enhance organic carbon export and CO2 sequestration. Until recently, few people believed that jelly organisms could play any major role in the carbon cycle, thus they have been excluded from large biogeochemical research programs. In consequence, the data available up to now are scarce and we are just starting to comprehend the fundamental properties that will allow us to better understand the role of jellyfish and pelagic tunicates in the global carbon cycle."

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